This is a series. Set in the Marvel Cinematic Universe universe.
A weapons manufacturer is ambushed with his own munitions, held in a cave and made to build a missile, and builds a powered suit instead. Back home he shuts the arms business down, rebuilds the suit properly, and finds that the man selling to both sides is his own business partner. It ends with him telling a press conference who he is, which no superhero film had let its hero do.